More image scanners that read an image of a document and electrically process the read image, or more printers that print an image, have employed a sheet feeding device that feeds a sheet such as a document from which an image is read or a paper sheet on which an image is printed to an image reading unit or a printing unit. The sheet feeding device feeds a document downstream by rotating a pickup roller, which has a relatively large frictional coefficient, while coming in contact with the document. Since the pickup roller feeds a document downstream using a frictional force with the document, sheet feeding devices in which a contact state of a document with the pickup roller is adjusted to appropriately feed the document, are known (for example, Japanese Laid-open Patent Publication No. 10-35897 and Japanese Laid-open Patent Publication No. 2007-137526.)
However, when a document properly comes in contact with the pickup roller at the time of feeding but documents are not properly set on a document mounting board, a problem, in which a document cannot be fed downstream due to non-contact of the document with the pickup roller, may occur at the time of feeding a document using the pickup roller. For example, as described in JP 10-35897 A, when a guide is disposed upstream from the pickup roller and a document is separated apart upward from the pickup roller by the guide turning upward on standby, documents may stop in a part of the guide turning upward at the time of setting documents and the documents may not reach the position of the pickup roller. In this case, even when the guide is lowered at the time of feeding a document, no documents is present at the position of the pickup roller and thus no document can be forwarded downstream. Accordingly, there is room for improvement in a structure for feeding a document without causing non-feeding.